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Question -What is static nested class and usage in Java

Solutions– Many developers are confused and telling static nested class as static inner class.But in java, there is no static inner class. 😮

Ok.First we understand ,

what is inner class – inner class or nested class is a class declared entirely within the body of another class or interface.An instance of a normal or top-level class can exist on its own. By contrast, an instance of an inner class cannot be instantiated without being bound to a top-level class.

class OuterClass {

  class InnerClass {  }

}

Types of nested classes in Java

Member class – They are declared outside a function (hence a “member”) and not declared “static”.
Local class
Anonymous class

Nested or inner class is a member of its enclosing class.
Non-static nested classes (inner classes) have access to other members of the enclosing class, even if they are declared private. Static nested classes do not have access to other members of the enclosing class.A static nested class interacts with the instance members of its outer class (and other classes) just like any other top-level class. In effect, a static nested class is behaviorally a top-level class that has been nested in another top-level class for packaging convenience.

Why we use– if a class does’nt depend on anything other than his outer class then we will create static nested class.for example – we have nThere is no need for LinkedList.Entry to be top-level class as it is only used by LinkedList (there are some other interfaces that also have static nested classes named Entry, such as Map.Entry – same concept). And since it does not need access to LinkedList’s members, it makes sense for it to be static – it’s a much cleaner approach.

Happy learning with Vinay in techartifact…

Can I override a static method? – No you cant

Many people have heard that you can’t override a static method. This is true – you can’t. However it is possible to write code like this:

class test {
    public static void method() {
        System.out.println("in test");
    }
}

class example extends test{
    public static void method() {
        System.out.println("in example");
    }
}

This compiles and runs just fine. Isn’t it an example of a static method overriding another static method? The answer is no – it’s an example of a static method hiding another static method. If you try to override a static method, the compiler doesn’t actually stop you – it just doesn’t do what you think it does.

lets try it

Briefly, when you override a method, you still get the benefits of run-time polymorphism, and when you hide, you don’t. So what does that mean? Take a look at this code:

class test{
    public static void classMethod() {
        System.out.println("classMethod() in test");
    }

    public void instanceMethod() {
        System.out.println("instanceMethod() in test");
    }
}

class example extends test {
    public static void classMethod() {
        System.out.println("classMethod() in example");
    }

    public void instanceMethod() {
        System.out.println("instanceMethod() in example");
    }
}
 
class Test {
    public static void main(String[] args) {
        test f = new example();
        f.instanceMethod();
        f.classMethod();
    }
}

If you run this, the output is

instanceMethod() in example
classMethod() in test

Now we should understand what is overriding and hiding-

Overriding
An instance method overrides all accessible instance methods with the same signature in superclasses [JLS 8.4.8.1], enabling dynamic dispatch; in other words, the VM chooses which overriding to invoke based on an instance’s run-time type [JLS 15.12.4.4]. Overriding is fundamental to object-oriented programming and is the only form of name reuse that is not generally discouraged:

class Base {
    public void f() { }
}

class Derived extends Base {
    public void f() { } // overrrides Base.f()
}

Hiding
A field, static method, or member type hides all accessible fields, static methods, or member types, respectively, with the same name (or, for methods, signature) in supertypes. Hiding a member prevents it from being inherited.

class Base {
    public static void f() { }
}

class Derived extends Base {
    public static void f() { } // hides Base.f()
}

Instance methods and class methods have this important difference in behavior, we use different terms – “overriding” for instance methods and “hiding” for class methods – to distinguish between the two cases. And when we say you can’t override a static method, what that means is that even if you write code that looks like it’s overriding a static method (like the first test and example at the top of this page) – it won’t behave like an overridden method.

Tag: static

What is static nested class and usage in Java

Why we can’t override the static method? or Overriding Vs Hiding